A natural joint, such as a hip joint or a shoulder joint, may undergo degenerative changes due to a variety of etiologies. When these degenerative changes become so far advanced and irreversible, it may ultimately become necessary to replace a natural joint with a prosthetic joint. For example, when implantation of a hip joint prosthesis becomes desirable, the head of the natural femur can be first resected and a cavity can then be created within the intramedullary canal of the host femur for accepting the hip prosthesis. The hip prosthesis may be inserted and supported within the host femur by cementing the hip prosthesis within the host femur or by using an impact method where the hip prosthesis is tightly fit within and is supported by the host femur. If the acetabulum also needs repair, all or most remnants of articular cartilage can be generally removed from the acetabulum and an acetabular prosthesis which will accommodate the head or ball of the hip prosthesis can be affixed to the acetabulum. The acetabular prosthesis can be affixed to the acetabulum by means of cement, screws or other appropriate fixation means.
An acetabular prosthesis can include an acetabular shell component and a polymeric shell liner. The acetabular shell component can be stabilized using fixation screws to secure the acetabular shell to bone. The acetabular shell component can include a smooth inner concave surface, a roughened outer convex surface and a plurality of holes or ports passing therethrough for receipt of the fixation screws. The fixation screws can be installed into all of the holes or only some of the holes depending on the geometry and biology of the anatomy of the patient. The polymeric shell liner can seat against the smooth inner concave surface and can act as a bearing surface for the head of the hip prosthesis.
As the hip prosthesis is loaded, micro-motion may occur between the acetabular shell component and the polymeric shell liner, potentially resulting in wear debris being formed between the shell component and the shell liner. Since some of the holes in the shell component may not receive fixation screws, the wear debris may pass through these open holes and out of the shell component.
Examples of acetabular prosthetic implants are described in U.S. Pat. No. 4,955,325 to Zarnowski et al., U.S. Pat. No. 5,310,408 to Schryver et al., U.S. Pat. No. 5,782,929 to Sederholm, U.S. Pat. No. 5,925,077 to Williamson et al., and U.S. Pub. No. 2010/0057217 to Breimesser et al.